1. Field
This invention relates to circuits for supplying electrical power and, more specifically, relates to methods and apparatus for providing electrical power so as to increase the operating range of an electrical circuit.
2. Description of Related Art
Tunable Micro Electro-Mechanical Systems (MEMS) devices appear more and more in RF circuits. For example, such devices are frequently implemented in wireless communication systems. Tunable MEMS allow for new functionality, or for improved performance of such systems (e.g. the performance of electrostatically tuned variable capacitors) as compared to previous approaches. The use of tunable MEMS devices provides for improving the linearity of tunable RF filters or enhancing the phase noise behavior of voltage-controlled oscillators. However, the tuning voltage required by such devices is typically between 5V and 50V, which is much higher than the maximum supply voltage of deep sub-micron complementary metal oxide semiconductor (CMOS) technologies in which such MEMS devices may be implemented.
Although the required tuning voltage of tunable MEMS devices may be modified by making design changes, it is extremely difficult to achieve a tuning voltage that is at or below the maximum supply voltage of advanced (deep sub-micron) CMOS technologies. Further, the rapidly decreasing supply voltages of scaled CMOS technologies further complicates this concern. Moreover, there are design/performance trade offs between the tuning voltage and other parameters of MEMS devices (e.g., mechanical resonance frequency, electrical losses and linearity of the device). Given these concerns, it is common to provide (e.g., using a MEMS control circuit) tuning voltages that are higher than the supply voltage of the rest of the system (e.g., the supply voltage of the CMOS components, which may be less than 1.5 V).
One approach that is used is to directly apply a high voltage signal (the tuning voltage) to an output stage of a high voltage control circuit included in a MEMS control circuit. Such approaches may employ a dedicated high voltage device (e.g., Alcatel HBiMOS, available from Alcatel, Paris, France), such as is described in “Current drive methods to extend the range of travel of electrostatic microactuators beyond the voltage pull-in point” by R. Nadal-Guardia. et al. IEEE J. Microelectromechanical Systems, Vol.11, No.3, pp.255–263, Jun. 2002. Alternatively, dedicated high voltage devices may be implemented by making process modifications to a standard CMOS manufacturing technology (See e.g., “A 1.5-V-supplied CMOS ASIC for the actuation of an electrostatic micromotor”, P. Favrat et al., IEEE/ASME Trans. on Mechatronics, Vol.2, No.3, pp. 153–160, September 1997). Such dedicated high voltage devices and/or manufacturing process modifications are typically undesirable due to the cost associated with such approaches.